Draw forming

ABSTRACT

A stretch assembly or fixture for tensioning sheet metal stock in conjunction with draw forming. The stretch assembly supports the lower or bottom die member and has two upright stretch units, one on each of two opposite sides of the die. Each unit includes a work gripping head movable vertically relative to frame structure of the unit. A jaw assembly of each head is adapted to engage one of two opposite edges of a metal sheet to be formed and is movable relative to its head transversely of the vertical path of the head travel to stretch the sheet. Stretch links are pivotally connected between each jaw assembly and the frame structure of the respective stretch unit and move the jaw assemblies in a prescribed path transversely of the path of head travel in response to vertical movement of the gripping heads. The vertical position at which the links are pivoted on the stretch unit frame structure and the effective length of the links can be adjusted to control the movement of the gripping heads. The jaw assemblies include upper and lower jaw members. The upper members are supported for vertical movement to grip and release work and horizontal movement to expose the lower jaw to facilitate loading on extracting work.

United States Patent MacKenzie DRAW FORMING Robert A. MacKenzie, 8351 Lucerne Drive, Chagrin Falls, Ohio 44022 22 Filed: Dec.4, 1970 21 Appl.No.: 95,253

[72] Inventor:

[52] US. Cl ..72/305, 72/296, 72/31 1 1 July 18, 1972 Primary Examiner-Charles W. Lanham Assistant Examiner-Michael J. Keenan Attorney-Watts, l-lofimann, Fisher & Heinke ABSTRACT A stretch assembly or fixture for tensioning sheet metal stock in conjunction with draw forming. The stretch assembly supports the lower or bottom die member and has two upright stretch units, one on each of two opposite sides of the die. Each unit includes a work gripping head movable vertically relativeito frame structure of the unit. A jaw assembly of each head is adapted to engage one of two opposite edges of a metal sheet to be formed and is movable relative to its head transversely of the vertical path of the head travel to stretch the sheet. Stretch links are pivotally connected between each jaw assembly and the frame structure of the respective stretch unit and move the jaw assemblies in a prescribed path transversely of the path of head travel in response to vertical movement of the gripping heads. The vertical position at which the links are pivoted on the stretch unit frame structure and the effective length of the links can be adjusted to control the movement of the gripping heads. The jaw assemblies include upper and lower jaw members. The upper members are supported for vertical movement to grip and release work and horizontal movement to expose the lower jaw to facilitate loading on extracting work.

13 Claims, 13 Drawing Figures PATENTED JUL 1 8 1912 SHEET 2 BF 7 NdE INVENTOR. ROBERT A. MACKENZIE ATTOIZN 5Y5 PATENTED JUL 1 8 I972 SHEET 3 OF 7 INVENTOR. ROBERT A. MAC KENZI E SHEET N []F 7 INVENTOR. ROBERT A. MACKENZl E ATTOQ NEY9.

PATENTED JUL 1 8 I972 SHEET 5 [IF 7 5 wmv \x xxx FIG.6

INVENTOR. ROBERT A MACKENU E m ATTOQNEYS.

DRAW FORMING FIELD OF THE INVENHON This invention relates to a stretch assembly or fixture for gripping edges of sheet metal stock and stretching the stock to facilitate forming in a draw press or the like.

SUMMARY OF THE INVENTION The present invention provides a stretch assembly or fixture for use with a metal forming draw press and the like, which mechanically applies positive forces to movable gripping heads of the assembly and controls movement of the heads in a prescribed path to stretch a metal sheet by the use of stretch links that act independently from the die used to draw form the sheet. The stretch assembly is typically located on the bed of a draw forming press and may support a bottom draw forming die member. A mating upper die member is carried by a ram of the press, may be partially wrapped about the lower die member, and is then draw formed as the ram and upper die are lowered.

In the preferred embodiment of this invention, two upright stretch units are located at two opposite sides of the die area of the press each guiding a work-gripping head for vertical movement. A jaw assembly is carried in each head, movable transversely of the path of head movement toward and away from the die area of the press. A link is pivoted to a fixed frame portion of each upright stretch unit and to an associated jaw assembly. Typically two such links are provided for each unit. A sheet of metal to be formed is gripped in the jaw assemblies, initially above the lower die member. The gripping heads are then lowered hydraulically. As the heads are lowered the link or links associated with each jaw assembly causes the assembly to move a predetermined distance transversely of the path of the head movement away from the lower die member, toward the lower die member, or first in one direction and then the other, depending upon location of the link pivot point on the stretch unit and the effective length of the link, both of which can be varied, to obtain the desired movement of the associated jaw assembly. This facilitates the use of different dies both because the links are not connected between the die and the stretch assembly and because the links can be readily adjusted for the gripping head movement required for different dies.

The present invention also provides an improved gripping jaw construction that permits rapid and convenient loading and extracting of work. Each jaw assembly includes a lower jaw and a complementary upper jaw movable toward and away from the lower jaw to grip and release a marginal edge of a sheet of metal to be stretched. The upper jaw, in accordance with this invention, is also independently movable rearwardly of the front edge of the lower jaw that faces the die so that the lower jaw provides an upwardly facing surface unobstructed from above by the upper jaw to receive and support the work. In use, with the upper jaw spaced above and rearwardly of the lower jaw, the sheet to be stretched can be placed on the lower jaws and then gripped by moving the upper jaws fust forward into overlying relationship with the associated lower jaw and then downward. In a preferred embodiment, the upper jaw of each jaw assembly is movable rearwardly from the front edge of the lower jaw through pivotal movement about an axis perpendicular to the upper surface of the lower jaw so that the upper jaw swings back in a plane parallel to the support surface of the lower jaw. In the particular embodiment disclosed herein, the lower and upper jaws are made in two sections each extending half the length of the jaw with each section individually movable towards and from the die area of the press. This is especially advantageous with jaws that are shaped in a chevrom or V-shaped configuration, as shown herein.

In addition to the above features, apparatus embodying this invention has the ability to provide high speed quality production, to assure positive control of stretching forces and gripping head movement, precise maintenance of the overall size of the formed sheet, and the relieving of the sheet stock from the necessity of pulling the heads toward each other as the stock is drawn into the die cavity. The construction of the preferred embodiment of the invention further provides a unitary assembly that can be placed in a press and receive the lower die without requiring complex interconnections between the stretch units, press and dies.

For purposes of illustration, the present invention is described in connection with the forming of metal stock between drawing dies in an upright press wherein the ram travels vertically and the stretch units are positioned at opposite ends of the bottom die. It will be apparent that these positions and directions are not absolutes, but are for convenience in describing the relative positions and movements on the parts of the structure. In most cases it is desirable that two movable stretch heads be employed, but there are instances in which the stock can be held in fixed position at one end and only one stretch head moved for stretching the stock.

The above and other features and advantages of this invention will become more apparent as the invention becomes better understood from the detailed description of a preferred embodiment when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of a drawing die press embodying the present invention, with the parts in position to receive a metal sheet to be formed;

FIG. 2 is a front elevational view of the stretch assembly of FIG. 1 showing the gripping heads in an opened and upper position, ready to receive the metal stock.

FIG. 3 is a top plan view of the stretch assembly of FIG. 2;

FIG. 4 is a front elevational view of the stretch assembly of FIG. 2 showing the gripping heads in a closed and lowered position;

FIG. 5 is a fragmentary sectional view taken along the line 55 of FIGS. 2 and 3;

FIG. 6 is a fragmentary sectional view taken along the line 66 of FIGS. 2 and 3;

FIG. 7 is a fragmentary sectional view with portions in elevation taken along the line 77 of FIG. 3;

FIG. 8 is a view similar to that shown in FIG. 7, with the upper work gripping jaw in a forward and closed position;

FIG. 9 is a view similar to that shown in FIG. 7 but showing a gripping head of modified construction;

FIG. 10 is a diagrammatic view of a gripping head illustrating the manner in which the head movement can be varied by the pivot point of a link;

FIG. 1 1 is a fragmentary front elevational view similar to the left part of FIG. 2, but illustrating an alternative embodiment;

FIG. 12 is a view similar to FIG. 11 but showing parts in a different operating position; and

FIG. 13 is a plan view of the apparatus shown in FIG. 1 1.

DETAILED DESCRIPTION The invention is shown incorporated in a conventional upright hydraulic or mechanical press 10 having a bed 11 with upright guide members 12 arranged at the corners and guiding a ram 13 for vertical reciprocation. Referring more particularly to FIGS. 1 to 10, a stretch assembly 14, embodying the present invention, is supported on the press bed 1 1 and in turn supports a drawing die 15 that has a convex forming face. The press ram carries the complementary drawing die 16. The dies 15 and 16 define, when closed, a concavo-convex pattern into which sheet metal stock is drawn by the dies. The sheet stock is tensioned by the stretch assembly 14 along one dimension only, and conventional hold-down rings or other devices are not employed. The ram of the press shown is driven on its forming and return strokes by hydraulic cylinders and pistons having piston rods 18 secured to the ram.

The stretch assembly 14 grips a sheet to be formed along two opposite edges and holds the same above the lower die 15, and simultaneously stretches and lowers the sheet onto the lower die member 15 preparatory to draw forming by the closing of the dies 15 and 16. The assembly 14 includes a central bed 20 upon which the lower die member 15 is supported, and two stretch units 22, 23 connected to two opposite sides of the bed 20. Advantageously, the bed 20 is formed of a plurality of side-by-side sections 20a, see FIGS. 2 and 4, so that the width of the bed can be varied to accommodate difierent particular die members and to locate the stretch units 22, 23 suitable distances apart. Each stretch unit 22, 23 is essentially of the same construction, but may have differently shaped gripping jaws and may be adjusted to operate difierently one from the other where the dies are asymmetrical about a vertical plane mid-way between the two stretch units.

In the preferred embodiment shown the dies and 16 are asymmetrical and the movements of the gripping jaw assemblies toward and from the lower die 15 during each forming operation are different. The gripping jaw assembly of the left hand stretch unit 22 is moved a predetermined distance towards the die 15 and the gripping jaw assembly of the righthand stretch unit 23 is moved a predetermined distance away from the die 15 greater than that moved by the gripping jaw assembly at the left, thereby producing a desired stretch in the sheet being worked upon. Because of the similar construction of the two stretch units, however, only the stretch unit 22 will be described in complete detail.

The stretch unit 22 is comprised of an upright frame 26, a gripping head 28 movable vertically in the upright frame 26, a jaw assembly 30 carried by and movable relative to the gripping head toward and away from the lower die 15 or central die area of the stretch assembly bed, and two stretch links 32, 34 connected between the upright frame 26 and the jaw assembly 30. The upright frame 26 is secured to and fixed relative to the bed and has laterally spaced vertical guideways 36, 38 that constrain and guide the gripping head 28 in vertical movement. The frame also includes vertical guideways 40 and 42, laterally outward from the guideways 36, 38 for guiding adjustable pivots for the stretch links. If desired, the bed 20 may be omitted and the lower die and the stretch units directly fixed to the bed 1 1 of the press.

The gripping head 28 includes vertical guide surfaces 44, 46 that cooperate respectively with the vertical guideways 36, 38 of the fixed frame. The vertical guide surfaces 44, 46 are formed in side members 48, 50 of the head that are connected by a top plate 52 and vertical front and back plates 64, 65. Four tubular guide passages 58, 59, 60, 61, as best shown in FIG. 6, are formed in the side members 48, 50 of the head and extend perpendicular to the vertical guideways 36, 38 of the frame. Two hydraulic cylinders 62, 64 are supported by a plate 66 of the frame 26 of the stretch unit and have upwardly extending piston rods 68, 70 that are secured to the horizontal plate 52 and serve to raise and lower the gripping head 28. The plates 52 are also adapted to be contacted by the ram 13 of the press when the ram is in a lowered position to assist the cylinders in lowering the gripping head 28 to its bottom positron.

The jaw assembly includes a normally fixed or stationary but adjustable lower jaw 72 and a movable upper jaw 73 both supported by a jaw assembly frame member including a vertical plate 74 having three vertically spaced, forwardly extending horizontal ribs 75, 76, 77. Four slides 78, 79, 80, 81 extend rearwardly from the vertical plate 74 and are slidably received in the guide passages, 58, 59, 60, 61, respectively, of the gripping head 28. The piston rods of short stroke, reciprocating-type, single acting fluid pressure-actuated motors 82, 83 are fixedly connected to the rear or left-hand side of the vertical plate 74 adjacent to the opposite ends thereof and the lefthand ends of the cylinders thereof are connected to rearwardly extending horizontal arms 88, 89, respectively. Normally the right-hand ends of the motors 82, 83 are pressurized with the right-hand cylinder heads being held firmly against the rear or left-hand side of the plate 74 so that the motors move with the plate as a unit. Under some operating conditions, it may be desirable to reduce the pressure in the motors and allow the plate 74 together with the jaw assembly of which it forrm a part, to move toward the die area of the press. Alternatively, the arms 88, 89 may be directly connected to the plate 74, but the construction having the motors 82, 83 therebetween is preferred. The rear ends of the arms 88, 89 are in the form of a clevis and pivotally support sleeves 90, 91, respectively, on pairs of pivot pins 92, 94 carried thereby. The sleeves 90, 91 adjustably receive the links 32, 34 and the links can be secured in any adjusted position by a suitable set screw, key or the like.

The links 32, 34 extend forwardly from the sleeves 90, 91 toward the guide ways 40, 42 of the frame 26 and the forward end thereof are connected by pivot pins 96, 97 to vertically adjustable yokes 98, 99. The yokes 98, 99 slide in the vertical guideways 40, 42, respectively, of the fixed frame and are mounted on the upper ends of vertical screws 100, 101, respectively. The screws 100, 101 are selectively rotated to adjust the vertical positions of the pivots 96, 97 through locking-type worm wheel drives 104, 105, respectively, by electric motors 106, 107, respectively, on the frame 26 of the stretch unit. Operation of the motors in forward or reverse raises or lowers the yokes 98, 99 and hence the front pivot points of the stretch links.

From the above construction, it will be apparent that vertical movement of the gripping head 28 in response to actuation of the cylinders 62, 64 will carry the jaw assembly 30 in a vertical path constrained by the fixed guideways 36, 38. As the gripping head moves vertically, the stretch links 32, 34 will cause the jaw assembly to move horizontally relative to the gripping head, in a path determined by the length of the links 32, 34 and the vertical location of the pivot pins 96, 97.

The lower jaw 72 of the jaw assembly 30 may be a single member fixed to the jaw assembly frame but is preferably formed of two sections 72a, 72b, each movably supported between the top side of the flange 75 and the bottom side of the flange 76 of the plate 74 of the jaw assembly frame. Each section has a generally horizontal upper face provided with a longitudinally extending groove 112 near a front edge of the jaw. The upper jaw 73 is formed of two sections 73a, 73b, each including a work sheet engaging or gripping member 113 at the lower side of one of the horizontal body plates 114 adjacent the front edge thereof. The body plates 1 14 of the upper jaw sections are movably supported between the upper side of the intermediate flange 76 and the lower side of the top flange 77 on the plate 74. In the illustrated embodiment, the adjacent ends of the two sections 72a, 72b of the bottom jaw and the two sections 73a, 73b of the top jaw are pivotally connected to the plate 74 of the jaw assembly frame by pivot pins 119, extending through aligned apertures in the flanges 75, 76, 77 of the plate 74 and upper and lower jaw sections 72a, 73a and 72b, 73b, respectively. For any given job set up such as that illustrated the outer ends of the lower jaw sections 72a, 72b are moved or adjusted toward the die area of the press to a desired position so that the lower jaw assumes a V-shape or chevron-shape with the opposite sections or halves diverging outwardly from the center. The outer end of the jaw sections may be secured in their adjusted position as, for example, by set screws threaded into tapped apertures in the flange 75 near the outer ends thereof and engageable with the under side of the lower jaw sections or in suitable apertures therein. The movement or adjustment of the lower jaw sections can be accomplished manually or by power, as desired.

In the illustrated embodiment the outer end of the lower and upper jaw sections 72a, 73a are provided with apertures which may be aligned with apertures in the outer ends of the flanges 75, 76, 77 for the reception of the pins 119, 120 in the event that it is desired to have the jaw sections assume a reverse configuration as the chevron shape referred to and is the situation with respect to the right-hand jaw assembly 30' in the illustrated embodiment. The jaw construction, referred to, facilitates the manufacturing and handling of the jaws and reduces the cost as many of the parts are duplicates and/or interchangeable. Each upper jaw section 73a, 73b is also connected to the vertical plate 74 by a horizontally disposed, forwardly extending fluid actuator 122, 123, respectively, of the cylinder and piston type, connected by pivot pins 128, 129 to the plate 74. Each actuator has a forwardly extending piston rod 124, 125, pivotally secured to a vertical pin 126, 127, respectively, carried by each jaw section. The fluid actuators pivot the jaw sections about the pins 119, 120 between a retracted position shown in FIGS. 3 and 7 where the front edges are aligned in a common vertical plane, and a forward position as shown in FIG. 8 where the two sections are angularly related and overlie the two sections of the lower jaw 72.

The work-engaging and gripping member 113 at the front edge of the support plate 114 of each upper jaw section 73a, 73b is carried for vertical movement by a plurality of piston rods 132 that depend from vertically oriented hydraulic cylinders 134 carried by the plates 114 of the upper jaw sections. The work-gripping member 113 has a depending projection 136 that extends adjacent a front surface 137 and cooperates when the member 113 is lowered with the groove 112 in the lower jaw to grip a marginal edge of a sheet of metal to be stretched.

When the fluid actutors 122, 123 are actuated to withdraw the piston rods 124, 125, the upper jaw sections 73a, 73b are retracted from above the lower jaw 72 to expose the upper surface 110 of the lower jaw. This facilitates the placement or retraction of the marginal edge of a sheet to be gripped and stretched. When the sheet is properly placed on the lower jaws, the upper jaw sections are extended forwardly by the fluid actuators 122, 123 while the gripping member 113 is in its raised position. The hydraulic cylinders 134 are then actuated to lower the work-gripping member 113 of each jaw section 73a, 73b to timily clamp the marginal portion of the sheet between the upper and lower jaws. It will be readily apparent that jaw assemblies of this general construction can facilitate various particular jaw configurations, the V-shaped or chevron configuration of the jaws 72, 73 being but one example.

In the preferred embodiment, the jaws 72', 73 of the righthand jaw assembly 30' of the stretch unit 23 are of complementary shape to that of the jaws 72, 73 of the jaw assembly 30, with the pivot pins 119', 120' in the outer aligned holes in the flanges 75, 76, 77 and the lower and upper jaw sections. The adjoining end of the lower jaw section 72a, 72b are fixed in an outer position with respect to the die area of the press and the upper jaw sections are movable about the pivot pins 119, 120 by the motors 122, 123. In all respects, the stretch unit 23 is of identical construction to the stretch unit 22. As best illustrated in FIG. 3, the central point of the lower jaw 72. of the jaw assembly 30' extends farther forward or outwardly from the unit than do opposite end portions and the fluid actuators 122', 123' which are connected to the jaw sections 73a, 73b of the die 73' and to the plate 74' service to retract or extend the upper jaw sections 73a, 73b to overlie the lower jaw sections 72a, 72b in the same manner as previously described in connection with the jaw assembly 30.

By way of a further embodiment, a jaw assembly 30 is shown in FIG. 9 of the drawings, in which a lower jaw 72" extends straight across the width of the jaw assembly in place of the chevroned jaw 72 of assembly 30. The remaining structure is identical to that of the assembly 30 and the upper jaw sections 73a, 73b are maintained in retracted condition by the actuators 122, 123 to cooperate with the lower jaw 72'. This construction does not permit withdrawal of the upper jaw from above the lower jaw to accommodate placement or removal of work.

FIG. 10 diagrammatically indicates the path followed by the jaw assembly 30, 30 or 30" in response to a change in the vertical position of the pivot pins 96, 97, which are maintained in any adjusted position relative to the upright frame 26 during operation with any particular die. As shown by way of example, when the position of the pivot pin 96 is lowered from points Pl-P7, that is, from point P1 to point P7 thorough intermediate points P2-P6, and the effective length of the link 32 or 34 is maintained constant, the jaw assembly is moved through arcs Al-A7, respectively, indicated at both the rear of the arm 88 and the front of the jaw assembly. With reference to FIG. 2, the path of travel of the jaw assembly 30 is indicated by the line L1 and the path of the jaw assembly 30' is indicated by the line L2. The location of the jaw assemblies in the lower position is shown in FIG. 4. As will be apparent from the above explanation, the difierence in the paths L1 and L2 is produced by the different location of the fixed pivot points on the stretch units 22, 23 for the stretch links 32, 32'. Notwithstanding the inward movement of the jaw assembly 30 along the line L1, a sheet of metal stock gripped between the jaws will nevertheless be stretched, because at the same time the jaw assembly is moving inward, it is also moving downward and wrapping the sheet about the curvature of the lower die. Alternatively, the tension can be applied from the opposed stretch unit with one edge of the sheet merely retained by the other unit. The various manners in which a tension can be applied with such an arrangement will be apparent to those skilled in the art. For example, when the gripping heads are moved downward, the jaw assemblies may continue to be moved farther apart by the links or one or both may be moved inward toward the other during the lower portion of the downward movement to position the inner faces of the jaw assemblies adjacent the die. In some cases, movement of one jaw assembly may be outward or inward throughout its entire downward travel and that of the other head may be partly outward and then back inward toward the die. The particular movements can be readily predetermined from the particular article to be made and the pivot positions and the lengths of the links adjusted accordingly.

Preferably, in all cases, the links are adjusted so that the jaw assemblies move relatively apart to tension the stock somewhat to take out the ordinary sag and waviness without causing the tension to reach the elastic limit before the sheet engages the highest peak or portion of the forming die. This tension generally is maintained until the stock is engaged with the die or for a very limited time thereafter. Through subsequent movement of the jaw assemblies, the sheet stock is tensioned into a range above the elastic limit of the material. This tension is maintained as the sheet is wrapped about the surface of the lower die and may be maintained throughout the drawing of the sheet by the dies. If desired, the sheet may be tensioned above the elastic limit before contacting the forming surface of the lower die. In either event, the stock is tensioned above its elastic limit before its formation by the cooperation of the dies. In some operations it may be necessary or desirable to relax or release the tension as the dies come together. In these situations the pressure in the motors 82, 83 and/or the motors 82, 83' can be reduced and/or relieved. The present construction and arrangement provides the necessary flexibility for establishing the desired path of jaw movement and degree of stretch required for a particular purpose. It applies positive mechanical forces to the sheet material and accurately locates the jaws of the jaw assembly at a predetermined point relative to the lower die.

An alternative construction for supporting the jaw assemblies for movement with the gripping heads and transversely of the path of movement of the gripping heads in timed relation to the movement of the gripping heads is illustrated in FIGS. 1 1, 12 and 13. These figures merely show the left-hand stretch unit, designated 222, of a stretch assembly similar to the stretch assembly of the preferred embodiment and the jaw assembly 230 except for a portion of the frame is merely shown in phantom lines. The parts of the stretch unit shown in FIGS. 11, 12 and 13 which are duplicates of those of the preferred embodiment are designated by the same reference characters.

The stretch unit 222 is comprised of an upright frame 226, a gripping head 228 movable vertically in the upright frame 226, a jaw assembly 230 carried by and movable relative to the gripping head toward and away from the lower die or central die area of the press, and two link mechanisms, designated generally 232, 234, connected between the upright frame 226 and the jaw assembly for movably supporting the jaw assembly. The upright frame 226 has laterally spaced vertical guideways 236, 238 that constrain and guide the gripping head 228 in its vertical movement. The frame also includes vertical guideways 240, 242, laterally outward from the guideways 236, 238 for guiding adjustable pivots for jaw assembly supporting linkages 232, 234.

The gripping head 228 is provided with vertical guide surfaces formed on side members 348, 254 of the head and which cooperate respectively with the vertical guideways 236, 238 of the fixed frame. The side members 248, 250 of the head are connected by a top plate 252 and vertical front and back plates 254, 256. Two hydraulic cylinders 62, 64 are supported by the stretch unit and have upwardly extending piston rods that are secured to the underside of the horizontal plate 252 and serve to raise and lower the gripping head 228.

The jaw assembly 230 is essentially like the jaw assembly 30 of the preferred embodiment and includes a vertical jaw assembly frame plate 274 having rearwardly extending arms 276, 278 fixedly secured thereto adjacent opposite ends thereof. The rear or left-hand ends of the arms 276, 278 are connected to pivot pins 280, 282 extending therethrough and through the rear or left-hand ends of links 286, 288, the forward ends of which are connected by pivot pins 96, 97 to vertically adjustable yokes 98, 99 slidable in the vertical guideways 240, 242, respectively, and threadably supported on the vertical screws I00, 101, respectively. The screws 100, 101 are adapted to be selectively rotated, as previously described, by electric motors 106, 107, respectively. The pivot pins 280, 282, in addition to having the members 276, 286 and 278, 288 pivotally connected thereto respectively, also have the upward ends of generally vertical links 302, 304 connected thereto. The lower ends of the links 302, 304 are connected by pivot pins 306, 308 carried by bosses projecting from the rear or left-hand side of the plate 256 of the vertically movable gripping head 228.

The front or right-hand plate 254 of the gripping head 228 is rovided with forwardly projecting bosses which carry pivot pins 318, 320 to which the lower ends of links 322, 324 are connected The upper ends of the links 322, 324 are connected by pivot pins 326, 328 connected to rearwardly extending bosses on the rear or left-hand side of the plate 274. The pivot pins 280, 306, 318 and 326 form the four pivot corners of the parallel motion linkage mechanism 232 which, with the corresponding mechanism 234, maintains the plate 274 vertically during the vertical movement of the gripping head 228. The links 286, 288 cause the jaw assembly 230 to move transversely of the movement of the gripping head 228 is predetermined timed relation to the movement thereof and in a predetermined path similar to the path Ll of movement of the jaw assembly 30 of the preferred embodiment.

Like the link 32 of the preferred embodiment, the link 286 is normally horizontal with the result that the jaw assembly 230 moves inwardly toward the die area of the press as the gripping head 228 is moved downwardly by the cylinders 62, 64. While the links 286, 288, as shown, are nonadjustable in length it is to be understood that they may be made adjustable, if desired, and that various patterns or paths of movement of the jaw assembly 230 can be obtained by changing the lengths of the links 286, 288, and the position of the yokes 98, 99 along the screws 100, 101, etc.

The right-hand stretch unit, not illustrated, is similar in construction to the left-hand stretch unit 222, and, if desired, can be made to follow a path similar to the path L2 of the jaw assembly 30. In this event the links corresponding to the links 286, 288 will be inclined to the path of movement of the gripping head as are the links 32, 34 of the preferred embodiment.

While the preferred embodiments of the invention have been described in considerable detail, it is to be understood that they are merely illustrative of the invention and it is the intention to hereby cover all embodiments thereof which come within the practice of those skilled in the art to which the invention relates and the scope of the appended claims.

Having thus described my invention, what I claim is:

1. In a stretch unit for a draw forming press, a stationary frame adapted to be located adjacent one side of a drawing die, a work-gripping head supported by said frame for movement relative to the frame, a work-gripping jaw assembly supported by said head for movement transversely of said head movement, and link means pivotally connected at one location to said frame and at another location to said workgripping jaw assembly to move the jaw assembly transversely of said head in response to movement of the head relative to the frame.

2. In a stretch assembly for a draw forming press, two

stretch units spaced apart and opposite each other, each unit including a stationary frame, a work-gripping head movable relative to the frame, guide means on said frame guiding said head in its movement relative to said frame, a work-gripping jaw assembly movable transversely of the movement of said head toward and away from the opposite stretch unit, means to move said work-gripping head independently of the head of the other stretch unit, and at least one link member pivotally connected between said work-gripping jaw assembly and said stationary frame to move said work-gripping jaw assembly transversely of the movement of said head in response to movement of said head relative to said frame. 3. In a stretch assembly for a draw forming press: a stretch assembly bed with a central area for supporting a drawing die; and stretch units extending upward on two opposite sides of the bed, each unit including a stationary frame portion, a work-gripping head movable relative to said frame portion along a path normal to the plane of said central area, means on said frame portion, means to move said head relative to said frame portion along said path, a work-gripping jaw assembly including opposed jaws supported by said head for movement transversely of said path of head movement toward and away from said central area, means on said jaw assembly to open and close said opposed jaws, and link means pivotally connected at one location to a said stationary frame portion and at another location to said work-gripping jaw assembly to move said jaw assembly relative to said head in response to movement of the head relative to said frame portion.

4. In a stretch assembly for a draw forming press, two stretch units spaced apart and opposite each other, each unit including a stationary frame, a work-gripping head movable relative to the frame, guide means on said frame guiding said head in its movement relative to said frame, work-gripping jaw assembly movable transversely of the movement of said head toward and away from the opposite stretch unit, means to move said work-gripping head independently of the head of the other stretch unit, and at least one link member extending between said workgripping jaw assembly and said frame, means pivotally securing one end of said link member to said frame, means pivotally securing said link member to said work-gripping jaw assembly, and means to adjust the vertical position of said means pivotally securing said link member to said frame.

5. In a stretch assembly for a draw forming press, two stretch units spaced apart and opposite each other, each unit including a stationary frame, a work-gripping head movable vertically relative to the frame, guide means on said frame guiding said head in vertical movement, work-gripping jaw assemblies movable horizontally toward and away from the opposite stretch unit, means to move the work-gripping head vertically independently of the head of the other stretch unit, and at least one link member extending between the workgripping jaw assembly and the upright frame, means pivotally securing one end of said link member to said frame, means pivotally securing said link member to said work-gripping jaw assembly, means to adjust the vertical position of said means pivotally securing the link member to the frame, and means to adjust the distance along said link member between said means pivotally securing said link member to the frame and to the work-gripping jaw assembly.

6. In a stretch unit for gripping an edge portion of sheet metal stock to be formed in a draw forming press, complementary gripping jaws adapted to receive and grip sheet metal stock, means for producing relative movement between said gripping jaws toward and away from one another to engage and release an edge portion of sheet metal stock located between said jaws, and means connected to one of said jam for moving said one jaw relative to the other jaw in a direction normal to that in which said jaws are moved to grip and release sheet metal stock to facilitate loading and extracting sheet metal stock.

7. Apparatus as set forth in claim 6 wherein said lower gripping jaw has an upper surface that generally defines a first plane and said upper gripping jaw is pivotally movable in a second plane parallel to the first.

8. Apparatus as set forth in claim 6 wherein said gripping jaws are located above and below one another and extend generally horizontally, said lower jaw has a front edge with two portions angularly related in a common generally horizontal plane, wherein the length of said upper jaw extends in a plane generally parallel to that of said lower jaw and includes two sections supported for pivotal movement relative to said lower jaw in the plane of said upper jaw at a point adjacent one end of said section, and wherein said means for moving said upper gripping jaw comprises means for pivoting each of said two sections relative to said lower jaw in the plane of said upper jaw.

9. In a stretch assembly for a draw forming press, two stretch units spaced apart and opposite each other, each unit including: a stationary frame, a work-gripping head movable vertically relative to the frame, means on said frame to guide said work-gripping head in vertical movement, means to move said work-gripping head vertically relative to said frame, a work-gripping jaw assembly movable horizontally toward and away from the opposite stretch unit and including complementary upper and lower work-gripping jaws providing a jaw opening facing forwardly toward the opposite stretch unit and adapted to receive and grip an edge portion of sheet metal stock to be formed by said press, means carried by the jaw assembly to move the upper work-gripping jaw vertically relative to the lower jaw to engage or release an edge portion of sheet metal stock to be formed in said press, means carried by the jaw assembly to move the upper gripping jaw of said unit rearwardly relative to said lower gripping jaw away from said opposite stretch unit and independently of said means to move the upper jaw vertically to facilitate loading and extracting sheet metal stock, and at least one link pivotally connected at one location fixed relative to said frame and at another location to said jaw assembly to move the jaw assembly transversely of the gripping head in response to vertical movement of the gripping head relative to the frame.

10. Apparatus as set forth in claim 9 wherein-said lower gripping jaw has an upper surface that generally defines a first plane and said upper gripping jaw is pivotally movable in a second plane parallel to the first.

1 1. Apparatus as set forth in claim 9 wherein said upper and lower gripping jaws extend generally horizontally, said lower jaw has a front edge with two portions angularly related in a common generally horizontal plane, wherein the length of the upper jaw extends in a plane generally parallel to that of the lower jaw and includes two sections supported for pivotal movement relative to the lower jaw in the plane of said upper jaw at a point adjacent one end of each section, and wherein said means for moving said upper gripping jaw comprises means for pivoting each of said two sections relative to the lower jaw in the plane of said upper jaw.

12. In a stretch unit for gripping an edge portion of sheet metal stock to be formed in a draw forming press, a stationary frame structure having guide surfaces, a first member movable along said guide surfaces and having guideways extending transversely of said guide surfaces, means to move said first members along said guide surface, a jaw assembly including work-gripping jaws and a second member supported for movement along said guideways, and a link pivotally secured to the jaw assembly and the frame structure for movin the jaw assembly along the guideways when said first mem er is moved along said guide surfaces.

13. In a stretch unit for gripping an edge portion of sheet metal stock to be formed in a draw forming press, a stationary frame structure having guide surfaces, a member movable along said guide surfaces, means to move said member relative to said frame structure along said guide surfaces, a jaw assembly including work-gripping jaws, means including a parallel motion mechanism connecting said jaw assembly to said member for movement transversely of the path of movement of said member, and a link pivotally secured to the jaw assembly and said frame structure for moving said jaw assembly transversely of the path of movement of said member when said member is moved along said vertical guide surfaces. 

1. In a stretch unit for a draw forming press, a stationary frame adapted to be located adjacent one side Of a drawing die, a work-gripping head supported by said frame for movement relative to the frame, a work-gripping jaw assembly supported by said head for movement transversely of said head movement, and link means pivotally connected at one location to said frame and at another location to said work-gripping jaw assembly to move the jaw assembly transversely of said head in response to movement of the head relative to the frame.
 2. In a stretch assembly for a draw forming press, two stretch units spaced apart and opposite each other, each unit including a stationary frame, a work-gripping head movable relative to the frame, guide means on said frame guiding said head in its movement relative to said frame, a work-gripping jaw assembly movable transversely of the movement of said head toward and away from the opposite stretch unit, means to move said work-gripping head independently of the head of the other stretch unit, and at least one link member pivotally connected between said work-gripping jaw assembly and said stationary frame to move said work-gripping jaw assembly transversely of the movement of said head in response to movement of said head relative to said frame.
 3. In a stretch assembly for a draw forming press: a stretch assembly bed with a central area for supporting a drawing die; and stretch units extending upward on two opposite sides of the bed, each unit including a stationary frame portion, a work-gripping head movable relative to said frame portion along a path normal to the plane of said central area, means on said frame portion, means to move said head relative to said frame portion along said path, a work-gripping jaw assembly including opposed jaws supported by said head for movement transversely of said path of head movement toward and away from said central area, means on said jaw assembly to open and close said opposed jaws, and link means pivotally connected at one location to a said stationary frame portion and at another location to said work-gripping jaw assembly to move said jaw assembly relative to said head in response to movement of the head relative to said frame portion.
 4. In a stretch assembly for a draw forming press, two stretch units spaced apart and opposite each other, each unit including a stationary frame, a work-gripping head movable relative to the frame, guide means on said frame guiding said head in its movement relative to said frame, work-gripping jaw assembly movable transversely of the movement of said head toward and away from the opposite stretch unit, means to move said work-gripping head independently of the head of the other stretch unit, and at least one link member extending between said work-gripping jaw assembly and said frame, means pivotally securing one end of said link member to said frame, means pivotally securing said link member to said work-gripping jaw assembly, and means to adjust the vertical position of said means pivotally securing said link member to said frame.
 5. In a stretch assembly for a draw forming press, two stretch units spaced apart and opposite each other, each unit including a stationary frame, a work-gripping head movable vertically relative to the frame, guide means on said frame guiding said head in vertical movement, work-gripping jaw assemblies movable horizontally toward and away from the opposite stretch unit, means to move the work-gripping head vertically independently of the head of the other stretch unit, and at least one link member extending between the work-gripping jaw assembly and the upright frame, means pivotally securing one end of said link member to said frame, means pivotally securing said link member to said work-gripping jaw assembly, means to adjust the vertical position of said means pivotally securing the link member to the frame, and means to adjust the distance along said link member between said means pivotally securing said link member to the frame and to the work-gripping jaw assembly.
 6. In a stretch unit for gripping an edge portioN of sheet metal stock to be formed in a draw forming press, complementary gripping jaws adapted to receive and grip sheet metal stock, means for producing relative movement between said gripping jaws toward and away from one another to engage and release an edge portion of sheet metal stock located between said jaws, and means connected to one of said jaws for moving said one jaw relative to the other jaw in a direction normal to that in which said jaws are moved to grip and release sheet metal stock to facilitate loading and extracting sheet metal stock.
 7. Apparatus as set forth in claim 6 wherein said lower gripping jaw has an upper surface that generally defines a first plane and said upper gripping jaw is pivotally movable in a second plane parallel to the first.
 8. Apparatus as set forth in claim 6 wherein said gripping jaws are located above and below one another and extend generally horizontally, said lower jaw has a front edge with two portions angularly related in a common generally horizontal plane, wherein the length of said upper jaw extends in a plane generally parallel to that of said lower jaw and includes two sections supported for pivotal movement relative to said lower jaw in the plane of said upper jaw at a point adjacent one end of said section, and wherein said means for moving said upper gripping jaw comprises means for pivoting each of said two sections relative to said lower jaw in the plane of said upper jaw.
 9. In a stretch assembly for a draw forming press, two stretch units spaced apart and opposite each other, each unit including: a stationary frame, a work-gripping head movable vertically relative to the frame, means on said frame to guide said work-gripping head in vertical movement, means to move said work-gripping head vertically relative to said frame, a work-gripping jaw assembly movable horizontally toward and away from the opposite stretch unit and including complementary upper and lower work-gripping jaws providing a jaw opening facing forwardly toward the opposite stretch unit and adapted to receive and grip an edge portion of sheet metal stock to be formed by said press, means carried by the jaw assembly to move the upper work-gripping jaw vertically relative to the lower jaw to engage or release an edge portion of sheet metal stock to be formed in said press, means carried by the jaw assembly to move the upper gripping jaw of said unit rearwardly relative to said lower gripping jaw away from said opposite stretch unit and independently of said means to move the upper jaw vertically to facilitate loading and extracting sheet metal stock, and at least one link pivotally connected at one location fixed relative to said frame and at another location to said jaw assembly to move the jaw assembly transversely of the gripping head in response to vertical movement of the gripping head relative to the frame.
 10. Apparatus as set forth in claim 9 wherein said lower gripping jaw has an upper surface that generally defines a first plane and said upper gripping jaw is pivotally movable in a second plane parallel to the first.
 11. Apparatus as set forth in claim 9 wherein said upper and lower gripping jaws extend generally horizontally, said lower jaw has a front edge with two portions angularly related in a common generally horizontal plane, wherein the length of the upper jaw extends in a plane generally parallel to that of the lower jaw and includes two sections supported for pivotal movement relative to the lower jaw in the plane of said upper jaw at a point adjacent one end of each section, and wherein said means for moving said upper gripping jaw comprises means for pivoting each of said two sections relative to the lower jaw in the plane of said upper jaw.
 12. In a stretch unit for gripping an edge portion of sheet metal stock to be formed in a draw forming press, a stationary frame structure having guide surfaces, a first member movable along said guide surfaces and having guideways extending transversely of said Guide surfaces, means to move said first members along said guide surface, a jaw assembly including work-gripping jaws and a second member supported for movement along said guideways, and a link pivotally secured to the jaw assembly and the frame structure for moving the jaw assembly along the guideways when said first member is moved along said guide surfaces.
 13. In a stretch unit for gripping an edge portion of sheet metal stock to be formed in a draw forming press, a stationary frame structure having guide surfaces, a member movable along said guide surfaces, means to move said member relative to said frame structure along said guide surfaces, a jaw assembly including work-gripping jaws, means including a parallel motion mechanism connecting said jaw assembly to said member for movement transversely of the path of movement of said member, and a link pivotally secured to the jaw assembly and said frame structure for moving said jaw assembly transversely of the path of movement of said member when said member is moved along said vertical guide surfaces. 